Water soluble protein materials

ABSTRACT

Dispersed insoluble plant proteins are digested with acid active enzymes under quiescent acidic conditions to completely dissolve the insoluble colloidal protein within the reaction medium. Following the digestion, the reaction medium is centrifuged and freeze-dried to form a soluble proteinaceous powder. The soluble protein can be included within carbonated or non-carbonated acidic beverages.

United States Patent 191 Pour-e1 et al.

l l 3,713,843 [451 Jan. 30, 1973 WATER SOLUBLE PROTEIN MATERIALSInventors: Akiva Pour-e1, St. Paul; Thoma 5 C. Swenson, Bloomington,both of Minn.

Assignee: Archer Daniels Midland Company,

Minneapolis, Minn.

Filed: Nov 30, 1971 Appl. No.2 203,443

Related U.S. Application Data Continuation of Ser. No. 797,669, Feb. 7,1969, abandoned.

U.S. CL; ..99/79, 99/17, 99/28 Int. Cl. ..A23l 1/00, A23j 1/14 Field ofSearch ..99/28, 79, 17, 14; 195/29;

Primary Examiner-Joseph Scovronek Assistant Examiner-Stephen B. DavisAttorney-Plumley, Tyner & Sandt [57] ABSTRACT Dispersed insoluble plantproteins are digested with acid active enzymes under quiescent acidicconditions to completely dissolve the insoluble colloidal protein withinthe reaction medium. Following the digestion, the reaction medium iscentrifuged and freeze-dried to form asoluble proteinaceous powder. Thesoluble protein can be included within carbonated or non-carbonatedacidic beverages.

- '9 Claims, No Drawings WATER SOLUBLE PROTEIN MATERIALS Thisapplication is a continuation of Ser. No. 797,669, filed Feb. 7, i969,and now abandoned.

This invention relates to water soluble proteins and particularly towater soluble plant proteins which are adapted for use in beverages. Aparticularly significant embodiment of the invention relates to an acidpH beverage which contains a modified soybean protein in clear solution.

Many efforts have been made in the recent years to develop high proteinfood materials which are adapted for specific nutritional aims.Particularly pertinent among these developments are the so-called healthfoods which are adapted to reduce the consumption of carbohydrates whilemaintaining the nutritional value of the products consumed. Oneparticular problem with these solutions'is that proteins which are usedto supply the required nutritional values are generally insoluble oronly partially soluble in the beverages as marketed. Since the consumergenerally requires not only a product which is nutritionally acceptable,but

one which is aesthetically acceptable, it has been desirable to producebeverages in the form of clear solutions. Thus, the consumer isattracted by the combined nutritional value of the product and theclean, clear appearance of the product. For reasons other than consumerattraction, it is also desirable to have clear solutions for ease inpackaging. Processing equipment can be adapted much more readily tohandle solutions than to handle dispersions or emulsions since thelatter tend to form sediments which clog flow lines and pumps.

In the past,proteins have not been adapted for use in beverages havingacid pH since they do not completely dissolve to form sparkling clearsolutions. Simple proteins, e.g. globulins, are insoluble in aqueoussolutions and even the relatively soluble secondary and primarydigestion products of simple proteins, e.g., proteoses and peptones, donot dissolve enough to give clear solutions Additionally, proteins varyin their solubility characteristics. Generally, proteins are leastsoluble at their isoelectric point which is the pH at which proteins areelectrically neutral. As the pH is changed from the isoelectric point tomore acid or more alkaline values, the protein becomes relatively moresoluble. This is true of the generally insoluble plant globulins (simpleproteins) and of the relatively soluble peptones and proteoses, etc.(primary and secondard split-products). The increased solubilityat acidof alkaline pH generally thought to be caused by the formation ofproteinates or protein-salts which are soluble salts of proteins formedby the reaction of the,

ionizable groups in the protein molecule with ions produced by the baseor acid, respectively. However, it will be apparent thatsince thecationic content of the protein is generally low, it is not possible toobtain substantially complete solubility of the protein by adjusting thepH. it is further apparent that extremely acid or extremely basicsolutions are not adapted for consumption. Thus, even though conversionof plant globulins to lower derivatives generally increases the proteinsolubility and even though decreasing pHfurtherincreases solubility, ithas not been possible to produce sparkling clear solutions of proteinsat pH in the range of 2-3 since the increased solubility is not adequateand since proteins are difficult to dissolve due to physical parameters.

Accordingly, it is the primary object of the present invention toprovide a protein which is adapted for forming sparkling clear solutionsat acid pH.

Another object is to provide a process for forming the water-solubleproteins from plant globulins, particularly from soybean protein.

Still another object is to provide a process for forming acid solubleprotein by reacting an insoluble protein with an acid active enzyme atacid pH.

Still another object is to provide a process which is comprised oftreating an insoluble plant protein at a pH which corresponds to the pHof intended solubility.

Yet another object of the invention is to provide a beverage which isadapted to have an acid pH and to contain in a sparkling clear solutionup to 20 percent of a modified plant globulin.

Still another object is to provide a process for converting insolublesoybean proteins into a substantially completely acid soluble proteinwith greater ease of dissolution.

These objects are accomplished in accordance with the present inventionby treating a dispersed plant globulin with an acid active enzyme atacid pH with controlled agitation wherein the enzyme digests the plantproteins in colloidal suspension and produces a protein which'isapproximately percent soluble in the reaction medium and wherein the pHof the reaction medium is approximately the pH of the beverage intendedto contain the thus treated protein. The invention thus involves aproteolysis performed at a specific pH range.

ltwill thus be seen that the present invention provides a method fortreating the simple proteins (globulins) with enzymes to digest suchsimple proteins and form the primary and secondary split-productderivatives thereof. These derivatives are proteins of a less complexnature and their digested products, which upon digestion by elementaryenzymes, will yield amino acids adapted for assimilation in the body.The treatment in accordance with the present inventionfacilitatesflsolutions of proteins in beverages, particu larlycarbonated beverages. Since the insoluble proteins are split and sincethe pH is strongly acidic,'the solubilizing tendencies of thesetreatments are combined with the increased solubility rendered by thisprocessLBy conducting the proteolysis at acid pH, it is and to be formedshould be illustrated. The proteins which are intended to be treatedareall plant globulins, i.e., simple proteins which yield onlyalpha-amino acids or their derivatives upon hydrolysis. Said simpleproteins are more particularly those vegetable proteins, such asglycinin, which are derived from soybeans. However, the invention isadapted to treat all globulins derived from plants. Plants, of course,include not only vegetables but cereals such as corn, wheat, rye, malt,and fruit kernels, etc. The invention will be described in terms of thetreatmentof soy proteins. The enzymes which may be used to treat theplant globulins are proteinases, i. e., those which are active inbreaking the piptide bond, particularly those which are active at acidpH of 2 to 5 such as fungal proteinases, pepsin, or any other acidactive enzyme. It is not intended to limit the invention to a specificenzyme nor to a specific protein since the invention lies in the processwhich enables one to produce a substantially completely acid solubleprotein from an insoluble protein.

Referring more specifically to the process, it should be pointed outthat the digestion medium provided is generally an aqueous dispersion ofprotein containing 3-6 percent protein in colloidal dispersion. Anysuitable acid may be added to the aqueous dispersion to provide theacidic pH required for digestion. An example is a combination of 6normal hydrochloric acid and concentrated phosphoric acid. The additionof the acid active enzyme is performed by stirring approximately 0.1 1percent based on the protein or 0.003 0.03 percent based on the totalslurry of the enzyme and allowing the reaction medium to settle. Duringdigestion, quiescent conditions .are maintained. Since the pH graduallyrises during digestion, it is sometimes necessary to add acid tomaintain a low pH. This pH adjustment is performed by periodicallyadding concentrated phosphoric acid or other acids to adjust the pH;adjusting to pH 2.7 is generally adequate. After sufficient time haselapsed for the colloidal protein to be digested and for the largersolids to settle out of solution, the digested protein slurry iscooledand centrifuged and the solid residue is discarded. The soluble materialis dried and renders a powdery product which is adapted for formingsparkling clear solutions at pH of approximately 2.7 to 4.75, indicatingsubstantially complete solubility. Other methods of recovering thesoluble matter are clearly adapted for use herein. To further illustratethe invention, the following specific embodi' ment is presented by wayof non-limiting example.

EXAMPLE Approximately 100 g of Nutrisoy 7-B (a commercially availablesoy protein flour) is extracted by mixing with about 20 times its weightin water at 96-l00 F for one hour with constant agitation. The resultingslur ry is allowed to settle and is decanted. The solid residue isextracted by mixing with approximately 10 times its weight of water forone hour at 96-l00 F with no agitation. The resulting slurry iscentrifuged and filtered and the solid residue discarded. Thesupernatent liquid from the first extraction and the second extractionare combined and hydrochloric acid is added to bring the pH of theliquid to 4.75. This liquid is centrifuged (filtering may be substitutedhere) and the super-natent liquid is discarded. The solid residue iswashed twice with 10 times its weight in water and the washings arediscarded. The washed solid residue is used to make a 3 percent solidsaqueous slurry to which is added a mixture of 6 normal hydrochloric acidand concentrated phosphoric acid to bring the pH to 3.5.

To the acid slurry is added 0.03% by weight based on the weight of theslurry of acid fungal proteinase with stirring. After settling themedium is left for a period of 2 days wherein the pH is periodicallyadjusted to about 2.7-4 by addition of concentrated phosphoric acid. Thedigestion medium is maintained in a generally quiescent state during thedigestion period except during the acid additions and the originallypresent colloidal dispersion gradually is converted into a sparklingclear phase. After the2 days, the digested protein slurry is cooled toabout 15 C, centrifuged, and the solid residue is discarded while thesupernatent liquid is converted by means of freeze drying into apowdered product. Upon adding the powdered product to water andadjusting the pH to from 2.7 to 4.75, the proteinaceous material issubstantially completely dissolved and forms a sparkling clear liquidwhen quantities up to 20% by weight of the soluble proteinaceousmaterial are used.

The above-noted example clearly illustrates that the protein which isinitially insoluble can be converted to a substantially completelysoluble material by treat ment according to the present invention.During the process, it is desirable to avoid allowing the pH to riseabove a point at which solubility occurs, this generally correspondingto the maximum pH at which the digested protein may be used, i.e., 4.75.During digestion, the pH naturally rises due to formation of theprotein-salts and concurrent consumption of acid, and additions ofphosphoric acid are intended to maintain the reaction pH at below 4.75.If the reaction is allowed to proceed to a point wherein the pH reaches4.75, the resulting product has a bad taste and is incompletely soluble.One explanation is that the colloidal solubility of soy protein islowest a pH of approximately 4.75. and since it is desired to keep thecolloidal sized protein dispersed for maximum digestion, it is desirableto avoid a pH of low solubility. It may further be desirable to maintainthe pH of the reaction medium at approximately the pH which will bepresent in the beverage. For example, if a beverage is intended to beproduced having a pH of 2.7 it is sufficient to maintain the pH of thereaction or digestion medium at approximately 2.7.

Another aspect of the process relates to the quiescent condition of thedigestion medium during the digestion period. Initially, agitation isprovided to mix the enzyme throughly throughout the dispersion; however,the dispersion should be allowed to settle and should be maintained in arelatively quiescent state during the entire digestion period, exceptthat some disruption occurs when acid is added. The material which islarger than colloidal size will thus be allowed to settle to the bottomand will be separated from the colloidal proteinaceous material which isintended to be treated by the process. A suitable time for digestion is6 hours to 1 week preferably on the order of l-2 days, for example, 15to 20 hours. The time of digestion depends on the activity of the enzymeused and the temperature of digestion; generally long time periods over4 days, for example, produce a bitter product with specific enzymes andare to be avoided, if possible. The concentration of enzyme based on theweight of the total mixture can range from 0.003 up to 0.03 percent byweight. Similarly, the concentration of the protein slurry treated maycontain protein in quantities of from 3 to 6 percent by weight. Themaximum efficiency is attained when the digestion medium is maintainedat approximately 40 C. However, other temperatures may be utilized witha somewhat reduced efficiency when the enzyme used dictates othertemperatures. Cooling after digestion is performed so as to precipitateinsolu ble material and avoid such. precipitation from beverages formedfrom the protein when the erages are refrigerated by the consumer.Cooling i mperatures from about 5 to 20 C is sufficient.

When a carbonated beverage is formed using the permanently solubleprotein (P.S.P.) of this invention, a suitable formulation is preparedas follows:

Flavored carbonated protein drinks were prepared using permanentlysoluble protein, (P.S.P.) produced by a variety of proteolylic enzymes.The following formulation was used:

1.4 g cool ade (any flavor) 62.5 g sugar 500.0 g carbonated 11,0

15.0 g P.S.P. The P.S.P. can be added either before or after addition ofthe carbonated water. The mixture should be stirred gently, to preventexcessive foaming, until all the P.S.P. is dissolved. The pH of thefinal solution will be between 2.5-3.0.

While carbonated beverages are referred to above as being the mostcommon acid beverages it should be understood that the invention extendsto non-carbonated acid" beverages. One such beverage is an orange drinkprepared as follows:

100 g reconstituted orange juice 3 g P.S.P. (permanently solubleprotein).

The ingredients are combined in either order. The mixture is stirredgently until all P.S.P. is dissolved. The final pH is between 3.0 and4.0.

Having described the invention in full, clear, and concise terms andhaving presented by way of nonlimiting example secured by Letters Patentis:

Which is claimed is:

1. The process for solubilizing insoluble plant proteins to make a clearsolution which comprises forming a dispersion of said protein in an acidmedium, adding an acid active enzyme, and allowing quiescent digestionto proceed until the insoluble colloidal protein is substantiallycompletely dissolved in the reaction medium.

2. The process of claim 1 wherein the plant protein is derived fromsoybean and is present in a quantity of from about 3 to 6 percent byweight.

3. The process of claim 1 wherein the reaction pH is maintained at 2.74.75.

4. The process of claim 1 wherein the enzyme used is active in acid pHof from 2 to 5.

5. The process of claim 1 wherein the time of reaction is from 15 to 20hours.

6. The process of claim 1 wherein the digestion product is subjected toclarification by centrifuging and freeze drying.

7. The product produced by the process of claim 1.

8. A clear aqueous. solution which has a pH in the range of 2.7 to,4.75and which contains up to 20 percent of a substantially completelydissolved modified plant protein produced by the processof claim 1 andwhich had been clarified by centrifuging to remove solid residue andthen dried. I I

9. The product of claim 8 wherein the solution is carbonated.

1. The process for solubilizing insoluble plant proteins to make a clearsolution which comprises forming a dispersion of said protein in an acidmedium, adding an acid active enzyme, and allowing quiescent digestionto proceed until the insoluble colloidal protein is substantiallycompletely dissolved in the reaction medium.
 2. The process of claim 1wherein the plant protein is derived from soybean and is present in aquantity of from about 3 to 6 percent by weight.
 3. The process of claim1 wherein the reaction pH is maintained at 2.7 - 4.75.
 4. The process ofclaim 1 wherein the enzyme used is active in acid pH of from 2 to
 5. 5.The process of claim 1 wherein the time of reaction is from 15 to 20hours.
 6. The process of claim 1 wherein the digestion product issubjected to clarification by centrifuging and freeze drying.
 7. Theproduct produced by the process of claim
 1. 8. A clear aqueous solutionwhich has a pH in the range of 2.7 to 4.75 and which contains up to 20percent of a substantially completely dissolved modified plant proteinproduced by the process of claim 1 and which had been clarified bycentrifuging to remove solid residue and then dried.